Question: Multiply the following complex numbers, marked as blue dots on the graph: $( e^{3\pi i / 2}) \cdot (3 e^{3\pi i / 2})$ (Your current answer will be plotted in orange.)
Explanation: Multiplying complex numbers in polar forms can be done by multiplying the lengths and adding the angles. The first number ( $ e^{3\pi i / 2}$ ) has angle $\frac{3}{2}\pi$ and radius $1$ The second number ( $3 e^{3\pi i / 2}$ ) has angle $\frac{3}{2}\pi$ and radius $3$ The radius of the result will be $1 \cdot 3$ , which is $3$ The sum of the angles is $\frac{3}{2}\pi + \frac{3}{2}\pi = 3\pi$ The angle $3\pi$ is more than $2 \pi$ . A complex number goes a full circle if its angle is increased by $2 \pi$ , so it goes back to itself. Because of that, angles of complex numbers are convenient to keep between $0$ and $2 \pi$ $3\pi - 2 \pi = \pi$ The radius of the result is $3$ and the angle of the result is $\pi$.